The present invention relates to a forming box to be used by dry forming of a fibrous tissue and encompassing an inlet for introduction of a fibre material which has been splitted up and chosen from amongst synthetic fibres and natural fibres and which is mixed into an airstream, and which forming box contains several revolving rollers, which are provided with radially placed spikes.
Various instruments of this type are known, for instance from the description of European Patent Application 0 159 618. The forming box in such a known plant will frequently be a part of the instrument, which makes an essential limitation for the capacity of the whole instrument.
In respect to the placing of the fibres on the underlying forming wire the forming box is provided with a bottom in form of a net or a sieve in the form of a bottom with a number of openings. In order to promote the passage of the fibres to the bottom of the forming box in the intention of achieving an increase of capacity the application of various mechanical elements has been proposed in form of wings and rollers or other scraping or brushing devices, which in an active way lead the fibres to the bottom of the forming box. Although such mechanical devices do give an increase of the capacity attempts have been made through many years to increase the capacity further.
The elaboration of meshes or openings in the bottom of the forming box has been decided from the fibres, which are used for the preparation of the fibrous tissue. There has primarily been some talk of using cellulose fibres in the manufacturing of paper products or nappy products. Thus, there has been a limitation of the length of the applied fibres. In practice it has thus not been possible to use fibres of lengths of more than 18 mm. This has simultaneously implied that there has been a limitation in the type of products that can be manufactured with such an instrument.